460 Sir Oliver J. Lodge [Feb. 28, 



while material inertia depends on those dimensions cubed, there 

 must be a size when the two are equal, i.e. when one might account 

 for the other. 



Write the charge in terms of electrostatic potential Y 



2KaV^ 



then 



3^2 



where c is l/V(/>tK), the velocity of light. 



Put this expression for m equal to |- -n a^ p, the ordinary mass. 

 Then the potential at which the two will be equal is 



which, for density of water and for a sphere 10"^^ centimetres radius, 

 is two volts ; quite a reasonable electrolytic value, such as is to be 

 expected among atoms.'"' 



The moral of this elementary but not very satisfactory argument 

 is that not for bodies of atomic size, but for something 100,000 



* The argument is plausible, and, taken as an illustration on ordinary lines, 

 will serve ; but considered seriously it may be quite fallacious, although the 

 main consequences which in the text are going to be drawn are correct. Few 

 things are more surprising than the extraordinarily large charge held by or 

 constituting an electron in proportion to its size. The charge is so large that 

 ordinary arguments about electricity as it exists on material spheres cannot be 

 expected to apply. If they did, or in so far as they do, the potential of 

 an electron would not be two volts but well over a million volts ; and the 

 density of the etherial substance of which it is presumably composed (if its 

 electric inertia is to be derived in any simple ordinary way from its bulk), 

 would have to be nothing like that of water, but of the order lO'^ q^ a billion 

 times the density of water. A thousand tons, in fact, to the cubic millimetre. 



We are here out of our depth among quantities on which a great deal of 

 work has to be done to reduce them to order. Yet it must not be supposed 

 that these figures are nonsensical. They require serious consideration ; and 

 that is all that can be said for them. I do not think there is any sense in 

 talking about the potential of an indivisible unit of charge, but we can talk 

 about the potential existing at the confines of an atom ; and that is a reason- 

 able magnitude, about 14 volts in the case of hydrogen, and not very different 

 for other elements. 



But on the other side of the subject everything points to the density of 

 ether being exceedingly high, though perhaps not so high as the above esti- 

 mate. It must at least be greatly denser than platinum or lead, and probably 

 immensely denser. 



A difficulty is often felt as to how ordinary matter like a planet can move 

 through such a medium without friction. Density however does not involve 

 viscosity ; the two are disconnected ; and resistance to mption would be caused 

 only by viscosity, of which the ether appears to have none. There are many 

 ways, more or less satisfactory, of picturing the perfectly free motion of matter 

 through an exceedingly substantial ether of space ; there would be innumerable 

 difficulties in supposing friction and consequent generation of heat. It is quite 

 certain that whatever tbe other does it does not dissipate energy. That imper- 

 fection belongs to the province of molecularly constituted matter. 



